1. Field of the Invention
The present invention relates to electromagnetic impulse transmission systems. In particular, the present invention relates to an electromagnetic impulse transmission system including a plasma antenna generator.
2. Description of Related Art
Electromagnetic energy can be used in many ways to sense objects from a distance. Radar, for example, is reflected electromagnetic energy used to determine the velocity and location of a targeted object. It is widely used in such applications as aircraft and ship navigation, military reconnaissance, automobile speed checks, and weather observations.
In certain situations, it is desirable to radiate one or more electromagnetic impulses to sense objects within the area, such as with conventional radar. Generally, as illustrated in FIG. 1, a signal generator 101 generates an electromagnetic impulse, which is radiated by an antenna 103 as an electromagnetic wave 105. Upon encountering an interface, such as an interface between an object 107 and air 109, a portion of the energy of electromagnetic wave 105 is reflected as an electromagnetic wave 111. Reflected electromagnetic wave 111 may then be received by a sensor 113, which analyzes reflected electromagnetic wave 111 to determine various characteristics of object 107.
As discussed above, only a portion of the energy of wave 105 is reflected as electromagnetic wave 111. The rest of the energy of electromagnetic wave 105 propagates into object 107 as electromagnetic wave 115. Upon encountering a second interface, such as an interface between object 107 and a second object 117 disposed within object 107, a portion of the energy of electromagnetic wave 115 is reflected as a second reflected electromagnetic wave 119. Second reflected electromagnetic wave 119 may then be received by sensor 113 to determine various characteristics of object 117. Impulse radar sensing uses these techniques for identifying characteristics of objects under ground, under water, within buildings, and the like.
It is often desirable to deploy such antennas, e.g., antenna 103, during flight. For example, a vehicle approaching an object may deploy an antenna so that electromagnetic energy may be directed toward the object. Conventional antennas generally include rigid or semi-rigid members that may be compactly folded for storage and transport and then unfolded when needed. Alternatively, conventional antennas may be wires that are explosively deployed or deployed by parachutes. A substantial amount of time is often required to deploy such antennas, which results in additional planning to determine the appropriate time to begin deployment so that the antenna will be available when needed. Further, circumstances may arise in which the immediate transmission of electromagnetic energy is desirable. If the antenna has not been deployed, there may not be sufficient time to deploy the antenna and transmit the electromagnetic energy in the desired time frame.
In other implementations, the vehicle from which the antenna is being deployed may be traveling at a very high rate of speed, for example, at a speed greater than the speed of sound. If the medium through which the vehicle is traveling has significant density, such as an atmosphere, considerable forces may act on such conventional antennas when deployed. It may, therefore, be very difficult, if not impossible, for such conventional antennas to be deployed without damage from fast-moving vehicles.
It is also desirable in certain situations to transmit electromagnetic energy having a broad spectrum of frequencies or to transmit low frequency electromagnetic energy. Generally, longer antennas are capable of transmitting electromagnetic energy more efficiently at lower frequencies than shorter antennas. Such longer antennas are typically capable of transmitting electromagnetic energy having higher frequencies as well. Longer, foldable antennas require more storage space, are typically more complex, generally take longer to unfold, and are typically more susceptible to damage upon deployment.
Sensing systems using short pulse (i.e., impulse), high energy sources need antennas that have a low ratio of electrical reactance to electrical resistance. Such antennas are commonly known as “low Q” antennas, as the ratio of electrical reactance to electrical resistance is represented by “Q.” Generally, the value of Q for an antenna is inversely proportional to the usable bandwidth for the antenna. Moreover, the use of antennas that have larger Q values in sensing systems employing short pulse, high energy sources may result in “antenna ringing”. Antenna ringing is undesirable, as it interferes with electromagnetic energy returned from objects or targets.
While there are many electromagnetic impulse sensing systems and antenna configurations for such systems well known in the art, considerable room for improvement remains.